Internal combustion engines, in particular diesel and gasoline engines, are frequently equipped with turbochargers. A turbocharger operates by compression of the intake airflow into the engine in order to achieve more power. In particular, a predetermined power can be generated by a turbocharged engine with a smaller displacement volume and thus smaller size and less weight, thereby achieving an increased specific power and a reduction of fuel consumption. In general, turbochargers are driven by the exhaust flow of the internal combustion engine. To this end, a turbocharger comprises a turbine arranged in the exhaust flow of the internal combustion engine, driving a compressor for compressing the intake airflow of the engine via a connecting drive shaft.
Recently, in particular for in-line engines, series sequential turbocharging has become popular. A regulated two-stage turbocharging system comprises a low-pressure (LP) stage for peak power and a high-pressure (HP) stage for performance and for fulfilling the back pressure requirements for driving exhaust gas recirculation (EGR), which is needed for NOx pollutant emission reduction. Moreover, the HP turbine usually is smaller and more responsive than the LP turbine. The HP and LP turbines are arranged sequentially in the exhaust flow of the internal combustion engine, the LP turbine being located downstream of the HP turbine. The LP and HP compressors are arranged sequentially as well, the HP compressor being located in the intake airflow downstream of the LP compressor.
The exhaust flow and the intake airflow are controlled by one or more bypass valves located in branches of the exhaust or intake system respectively. The bypass valves are parallel to their respective turbine or compressor. In particular, the exhaust flow may be controlled by a bypass valve of the HP turbine (turbine bypass valve, TBV) and a wastegate (WG) for bypassing the LP turbine. With the bypass valve closed, the respective turbine is driven maximally, while with the bypass valve partially or fully opened, the parallel branch is passed by at least part of the exhaust flow, the respective turbine being driven at a reduced rate. Similarly, the intake airflow may be controlled by a compressor bypass valve of the HP compressor (CBV). The bypass valves ensure a smooth operation of the engine and also ensure respecting various further constraints, concerning for example exhaust composition, compressor outlet temperature and turbine inlet temperature, as well as avoiding turbocharger surge or overspeed.
The bypass valves may be controlled actively, for example, electrically or by vacuum, and may comprise a position feedback sensor. As the HP turbine bypass valve (TBV) is important in emissions control, it is usually actively controlled and equipped with a position feedback sensor. The LP turbine bypass valve (WG) usually also is actively operated. For high speeds and loads, the wastegate (WG) actuator normally is used as a boost pressure limiter, hence high levels of accuracy are not required and consequently no position feedback is required for the WG. The compressor bypass valve (CBV) may be equipped for active actuation with position feedback, but for reasons of cost and complexity reduction, it usually is passive with no position feedback, e.g. it opens or closes due to the pressure difference across it, and, in particular, has two possible positions, which are the fully open and the fully closed positions.
The active valves usually have a default or “failsafe” position into which they move when there is no vacuum or electrical supply. The failsafe position normally is either fully open or fully closed. The default setting is determined by factors such as safety and engine power requirements at altitude. In particular, with a vacuum or electrical supply error, the TBV is fully open, and the WG is fully closed, in order to ensure minimal damage to the HP compressor and some basic driveability. In that case, the LP turbocharger is used, since the HP turbine is effectively bypassed. With a suitable calibration, it may be possible to achieve low particle emission even in this case.
However, this is not sufficient to ensure avoidance of compressor surge or overspeed, since these events can occur at exhaust lambda values greater than 1.2 (λ>1.2). In this case the valve actuators are inoperable and there is no effective boost pressure control for surge or overspeed protection. At altitude, this effect is more pronounced.
It is an object of the present disclosure to provide a method for operating an internal combustion engine equipped with a turbocharger arrangement, the method permitting increased turbocharger surge or overspeed protection in the case of turbocharger valve supply error. It is a further object of the disclosure to provide a control unit for an internal combustion engine with a turbocharger arrangement permitting increased turbocharger surge or overspeed protection in the case of such valve supply error.
A method of the present disclosure for operating an internal combustion engine refers to an internal combustion engine that is equipped with a turbocharger arrangement or turbocharger system comprising a low-pressure turbocharging stage and a high-pressure turbocharging stage, which are arranged sequentially. The low-pressure turbocharging stage comprises a low-pressure turbocharger which comprises a low-pressure turbine driving a low-pressure compressor. The high-pressure turbocharging stage comprises a high-pressure turbocharger, comprising, in particular, a high-pressure turbine driving a high-pressure compressor. The high-pressure compressor is arranged downstream of the low-pressure compressor in the intake airflow of the internal combustion engine. The low-pressure turbine is located downstream of the high-pressure turbine in the exhaust flow of the engine.
The turbocharger arrangement further comprises at least one turbocharger control valve for controlling the turbocharger arrangement. In particular, the low-pressure turbine may exhibit a low-pressure turbine bypass valve or wastegate (WG). The high-pressure turbine may exhibit a high-pressure turbine bypass valve (TBV). The at least one turbocharger control valve is configured to be actuated actively by a turbocharger valve supply system, which may comprise, for example, vacuum or electric transmission means. The at least one turbocharger control valve may be operated in a closed-loop control, employing the boost pressure for controlling the valve, for example.
The turbocharger arrangement may comprise further valves. Thus, for example, the high-pressure compressor may exhibit a compressor bypass valve (CBV). The CBV may be passive, e.g. operated by the pressure difference acting across it. The compressor bypass valve may be limited to two operational states, which are the fully open and the fully closed positions.
In accordance with the present disclosure it is determined whether the turbocharger valve supply system is in an operational state or in an error state. A supply system error, in particular an error of the electrical or vacuum system employed for actuating the at least one turbocharger control valve, may be detected by a diagnostic system in a standard engine control unit (ECU), which evaluates one or several sensor signals for detecting error modes. Additionally, an error of the turbocharger valve supply system may be detectable by a dedicated sensor system. An exemplary method for detecting an error mode of the wastegate, which may be indicative of a supply system error, is disclosed in EP 11155167.7, which is incorporated into the present application by reference.
According to a further aspect of the disclosure, a control unit for controlling a turbocharger arrangement of an internal combustion engine is configured to operate according to a method as described above. In particular, the control unit comprises at least one signal input port for capturing at least one sensor signal indicative of a turbocharger valve supply system error, or a diagnostic function for detecting a turbocharger valve supply system error based on other information available to the control unit. The control unit comprises at least one signal input port for capturing at least one sensor signal indicative of the low-pressure compressor flow, or is configured for determining the low-pressure compressor flow based on other information available. The control unit further comprises data processing means; the data processing means being configured for establishing a limit to an engine control parameter setpoint, depending on the low-pressure compressor flow. The processing means may be, in particular, configured for limiting fuel quantity or torque depending on the low-pressure compressor flow. The control unit may further comprise data storage means for storing a map or a lookup table, for example, employed in determining the limit to the engine control parameter. The control unit is further configured for feeding such modified control parameter setpoint to the engine control for controlling, for example, fuel quantity or torque according to the modified setpoint. The control unit may be, or may be part of, an electronic engine control unit (ECU).
Methods are provided for controlling an engine. One method may include adjusting airflow to a turbocharger arrangement with a turbine bypass valve bypassing a first turbine from a high-pressure turbocharger and a wastegate bypassing a second turbine from a low-pressure turbocharger; responsive to valve degradation, setting the turbine bypass valve fully open and the wastegate fully closed; and limiting engine torque based on a flow through a compressor of the low pressure turbocharger. In the event of valve degradation, limiting torque may prevent overspeed and surge of the low pressure turbocharger.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Further, the inventors herein have recognized the disadvantages noted herein, and do not admit them as known.